(where the Pi is too big)
revised 8 Jan 2015
Don't get me wrong -- I'd rather work with the Pi but the general purpose way they are packaged makes them too big to hold in your hand (Gee. And 18 months ago I thought they were tiny).
So, in addition to experimenting with them as semi-smart sensor front-ends to a Raspberry Pi I have explored some hand held applications.
Here's my first try:
Problems (least to most difficult):
1. The Arduino is too slow to include the accelerometer programming. After lots of tries, forget it. The user can tell the angle that she/he is holding the device.
2. The only buzzer/vibrators I could find (Adafruit: small, cheap) are actually tiny motors with unbalanced shafts. I had hoped that I could signal fairly small differences to the user (e.g.: 100ms buzz vs. 500ms). But, guess what, once you start these suckers spinning they stop when they feel like it. Disappointing, but not a fatal flaw (and I could always go to bluetooth audio). Revision: I just tried a 3rd wiring/programming scheme for the buzzers: using PWM I can signal 3 urgency levels with the vibrators.
3. I tried 5 distance/rangefinder devices: 3 ultrasonic, 2 active infrared, 1 laser. The overriding problem is that any of these gadgets can be fooled when held at an angle with the ground (the outgoing signal may be reflected instead of returned). Additionally, the laser only worked with the Raspberry Pi (used Pi's camera to measure pixel offset between the laser dot and the center of the camera sensor -- very accurate at 10'). As above, the laser dot can be reflected; also, a class III (i.e., safe) laser is blanked out in bright sunlight. All of the ultrasonics have too wide a beam of return. I settled for the 2nd IR device (Sharp-GP2Y0A02). It reads ok between 2' and 10'. But I get many goofy short returns. So I do 3 readings and choose the longest.
Anyway, my sample kind-of works most of the time. But even 99% of the time wouldn't be good enough.
Oh well. Onward. Here are 3 more ideas for hand-held devices:
The RFID devices are a pair. I need the reader to be able to test the detecter. The reader's 16x2 character display will show what was read -- presumably encoded. (Google "rfid hacking" if you're interested in [or paranoid on] the topic.)
The gas detectors and the RFID reader are all available from http://www.mpja.com/ for $10 or so each. An RFID detector can be home made.
My next projects!